SUBSEA CENTRIFUGAL COMPRESSOR WITH HORIZONTAL SHAFT AND WITH ONLY ONE AXIAL THRUST BEARING

Abstract

A centrifugal compressor unit including a motor having a rotor, at least one compressor having a shaft driven by the rotor; and a set of bladed wheels fitted on the driven shaft, the motor and the compressor being mounted in a common watertight casing. It further includes cooling means for cooling the motor, the cooling means having a gas cooler outside the casing. In operation, the motor, the compressor and the casing having the motor and the compressor are arranged horizontally, one axial thrust bearing only being provided on a compressor side.

Claims

1. A subsea centrifugal compressor unit, comprising: a motor having a rotor, at least one compressor having a shaft driven by the rotor; and a set of bladed wheels fitted on the driven shaft, the motor and the compressor being mounted in a common watertight casing, and further comprising cooling means for cooling the motor, the cooling means having a gas cooler outside the casing, wherein, in operation, the motor, the compressor and the casing having the motor and the compressor are arranged horizontally, and in that it further comprises one axial thrust bearing only on a compressor side.

2. The subsea centrifugal compressor unit according to claim 1, wherein the rotor and the driven shaft form one common shaft, the compressor unit having a set of three radial bearings for supporting the shaft, two bearings being provided on the motor side and one bearing being provided on the compressor side.

3. The subsea centrifugal compressor unit according to claim 1, wherein the rotor and the driven shaft are connected by means of a flexible coupling that is tortionally flexible and axially unflexible, and further comprising a set of four radial bearings for supporting each end of the rotor and the driven shaft.

4. The subsea centrifugal compressor unit according to claim 2, wherein the radial bearings for supporting the driven shaft or the rotor are magnetic bearings.

5. The subsea centrifugal compressor unit according to claim 1, wherein the axial bearing is a magnetic bearing.

6. The subsea centrifugal compressor unit according to claim 1, wherein the gas cooler is part of a closed loop extending partly outside the casing.

7. The subsea centrifugal compressor unit according to claim 1, comprising a seal between the motor, downstream the cooling means, and the compressor.

8. The subsea centrifugal compressor unit according to claim 1, wherein the casing is pressurized.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other objects, features and advantages of the invention will become apparent from the following description, given only by way of example and in view of the following drawings in which:

[0027] FIG. 1 illustrates the general features of a centrifugal compressor unit; and

[0028] FIG. 2 illustrates a further aspect of a centrifugal compressor unit.

DETAILED DESCRIPTION

[0029] FIG. 1 shows a centrifugal compressor unit 1 according to embodiments of the invention, for subsea applications, having a motor 2 and one or more compressor(s) 3 mounted in a common casing 4 leak tight to the gas manipulated by the compressor 3.

[0030] The casing 4 comprises two casing elements fixed together by appropriate attachment means, the one, denoted by numeral reference 5, accommodating the motor 2 and the other, denoted by reference 6, accommodating the compressor.

[0031] The casing elements are intended to provide support and protection for the motor and the compressor, respectively. As illustrated, the casing 2 is provided with a gas inlet orifice I facing the first compression stage of the compressor and an outlet orifice O facing the last compression stage.

[0032] In operation, the casing element assembly is intended to be pressurized and immersed and is arranged on a base such that the compressor unit is arranged horizontally.

[0033] In the exemplary embodiment, the motor 2 is formed by an electric motor, for example a high rotation speed motor (6000 to 16 000 rpm) supplied by a frequency variator and comprising a stator 7 and a rotor 8 supported by two radial end radial bearings 9 and 10.

[0034] As illustrated, the compressor 3 comprises a shaft 11 driven by the motor rotor and supported by a set of two radial end bearings 12 and 13 and a set of bladed wheels 14 mounted on the driven shaft and defining each a compression stage for the compressor.

[0035] Therefore, the rotor of the motor turns in two radial end bearings 9 and 10, whereas the compressor shaft turns in two radial end bearings 12 and 13.

[0036] In an embodiment, the bearings are rigidly fixed to the casing and are formed by active magnetic bearings that are controlled such that they can adapt to the dynamic behavior of the rotor or the driven shaft that they support.

[0037] As illustrated, the rotor 8 and the driven shaft 11 are linked via a flexible coupling that is radially flexible and axially unflexible to dynamically reduce the amplitude of the noise generated by ventilation when the compressor is rotated while efficiently propagating an axial thrust generated by the bladed wheels to the rotor of the motor.

[0038] As a matter of fact, in operation, the pressure differences generated at each compression stage generate a thrust on the driven shaft which is transmitted to an axial thrust bearing 16, for example an axial active magnetic bearing that is provided at the free end of the driven shaft 11, namely at the end opposite to the rotor of the motor 2.

[0039] As illustrated, in an embodiment, the axial bearing 16 is located on the compressor side, namely as close as possible of the active portion of the compressor shaft such that the axial bearing 16 is more appropriate to compensate for the thermal expansion of the shaft and to more accurately guarantee the axial position of the driven shaft and of the rotating bladed wheels within the second casing element 6.

[0040] It should be appreciated that thanks to the use of the flexible coupling that is tortionally flexible and axially unflexible, each of the rotor and the driven shaft can keep it on vibration behavior while the thrust generated during operation of the completion stages is supported by one first bearing only provided on the compressor side of the compressor unit.

[0041] In addition, with such an arrangement in which the rotor and the shaft are connected by a flexible coupling and having four radial bearings and one axial bearing, the compressor unit may comprise a large number of compression stages, namely above 3, and provide a high pressure ratio, namely above 3.

[0042] It has been noted that such a subsea compressor unit may provide a pressure between 80 and 150 bars.

[0043] For example, the compressor may comprise up to 8 compression stages and provide a pressure ratio up to 3 or 3.5.

[0044] Referring now to FIG. 2, in one embodiment, the subsea centrifugal compressor unit may be provided with cooling means for cooling the motor as well as the bearings.

[0045] In one embodiment, the subsea compressor unit may be provided with a cooling system having a cooling loop lying between the first compression stage and one side of the motor opposite to the compressor or lying between a both sides of the rotor, as illustrated, to provide cooling in closed loop.

[0046] In such a case, the cooling system comprises a gas cooler 18 lying outside the casing 2 and therefore in a contact with the cold deep water at constant temperature.

[0047] According to another embodiment, the cooling means may be arranged as an open loop with a clean gas supply 19 entering the first casing element 2 at one side of the rotor opposite to the compressor.

[0048] In such a case, the rotor may be provided with an additional bladed wheel 20 such that the clean gas supply is directed to the motor, through the radial bearing 9 and to the compressor through a barrier seal 21 provided between the flexible coupling 15 and the compressor.

[0049] Referring back to FIG. 1, an additional axial thrust bearing 17 may be used, in such a case, to compensate for the thrust generated by the motor internal pressure drop to the cooling flow.

[0050] At last, it should be noted that the invention is not limited to the disclosed embodiment.

[0051] As a matter of fact, according to the exemplary embodiments disclosed with reference to FIGS. 1 and 2, the compressor unit comprises a rotor and a shaft supporting the compression stages that are linked using a flexible coupling and having four radial bearings for supporting the respective free ends of the rotor and of the driven shaft.

[0052] According to another embodiment, the compressor unit may comprise a common rigid shaft or a rotor and a stator that are linked using a rigid coupling, namely a coupling that is axially and tortionally unflexible.

[0053] With such an arrangement, the common shaft may be supported by two radial bearings on the motor side and by one radial bearing at the compressor side, with one axial bearing only. This arrangement also permits to have a large number of compression stages, namely above 3, and provide a high pressure ratio, for example above 3.

[0054] This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.